Question

Q2. A. A synchronous machine driven by a diesel engine. The machine is connected to infinite bus and the active and reactive power supplied by the machine are monitored. Initially, the machine is supplying Si=P1+jQ1 to the infinite bus. Assuming the governor, exciter and the diesel engine are controlled manually, what sequential actions should be taken by the operator to make the active and reactive power as below. S2=P2+jQ1 where P2>P1, (b) S3=P2-jQ1, (c) S4=-P3-jQ1, (d) S5=-P3+jQ2. (12M)

Answer 1

Initial power supplied by the machine is

S1 = P1 + jQ1

Please note that diesel engine fuel input will change only active power , exciter controls reactive power supply and Governor control speed of the machine

(a) Now the power supplied by the machine became

S2 = P2 +jQ1 where P2>P1

So we have here increased Active power ,for this we need to increase fuel input to the generator others parameters maintaining constant

(b) Now power became

S3 = P2 - jQ1

Here machine is acting as an capacitor i.e. delivering reactive power so excitation is altered.

(c) Now power is

S4 = -P3 - jQ1

Machine is acting as an motor thats why active power is negative and Electrical input is taken by the motor.

others things are as of previous case

(d) Power is

S5 = -P3+ jQ2

Here excitation is changed , motor is acting as an inductor and absorbing reactive but excitation is more as of previous case